Metal oxide-hydrogen batteries, such as nickel oxide-hydrogen batteries, have seen wide use in aerospace applications because they are rechargeable, have an extremely long cycle life and provide a uniform output during the entire discharge cycle.
In the typical nickel oxide-hydrogen battery the positive electrodes are generally in the form of flat porous, sintered nickel plaques impregnated with nickel hydroxide, while the negative electrodes are formed of a fine nickel mesh screen having a catalyst, such as platinum black, bonded to one surface of the screen through a hydrophobic polymeric material. On discharge of the battery, hydrogen gas diffuses through the electrolyte surrounding the catalyst surfaces of the negative plates and becomes disassociated by the catalyst to the monatomic form. The monatomic hydrogen is ionized and combined with hydroxyl ions to form water with an electron being released in the process of forming each hydrogen ion. In addition, hydroxyl ions are formed at the positive electrode by the reaction of water with the available oxygen content of the nickel oxide. As a result of these reactions an electron current is produced in the exterior circuit.
On recharging the reaction is reversed, with the recharging being characterized by the regeneration of hydrogen gas at the negative electrode and the reoxidation of the nickel hydroxide at the positive electrode.
To reduce the volume of hydrogen gas required for reaction, the hydrogen is compressed within an outer pressure vessel that contains the electrodes. In the past, the outer vessel has been composed of a high strength corrosion resistant alloy, such an Inconel. However, the fabrication of a pressure vessel from an alloy such as Inconel is extremely expensive. Further, different applications of use of the metal oxide-hydrogen battery have different pressure requirements and thus there is no standardized wall thickness for the Inconel vessel.
Because of these problems, it has been proposed to construct the pressure vessel of a thin-walled liner formed of a material which is impervious to the passage of hydrogen gas and then to wrap the liner with hoop or cylindrical and helical windings of fibrous material impregnated with a thermosetting resin to provide the necessary strength for the particular application of use. In a vessel of this type, the inner liner can either be formed of a thin layer of a metal, such as Inconel or stainless steel, or it can be a polymeric film, as described in U.S. Pat. No. 4,923,769. The use of an outer fiber reinforced resin layer has the advantage that the strength for any particular application of use can be readily varied by increasing or decreasing the amount of windings in the outer layer, and by the use of different winding patterns.
To improve the performance of the battery, heat transfer fins have been incorporated with the cell modules to increase the transfer of heat from the cell modules to the vessel wall and hence to the exterior. However, a fiber reinforced resin outer layer restricts the transfer of heat to the exterior. It is recognized that the heat transfer of the outer layer is adequate in the X and Y directions, which are parallel to the fiber orientation, because the fibers, which can be graphite or glass, act as heat conductive cores. However, the heat transfer in the Z direction, which is in the direction of the wall thickness, is relatively poor. Attempts have been made to increase the heat transfer in the Z direction by abrading the fibrous material to provide minute fibrils on the fibers, or by varying the winding pattern. However, these attempts have not appreciably increased the heat transfer through the outer fiber reinforced resin layer of the vessel.